The present invention relates to implants for the correction of anatomic segments of the human foot. In particular, the invention provides means for lengthening the lateral column of the foot.
The foot is a complex structure of skeletal components and ligaments that interact to produce walking, running and jumping motions, and that act as a shock absorber during these motions. The foot often absorbs up to 2½ times the body weight in load. Subtalar joint pronation is a complex motion that is typically invoked during a heel strike. Pronation effectively “unlocks” the bones of the foot to render it loose and mobile so that the foot can effectively adapt to the supporting surface. Proper pronation facilitates flexion of the knee during walking and running.
On the other hand, supination is essentially the opposite of pronation and is a motion that effectively “locks” the bones of the foot to convert the foot into a more rigid lever in preparation for the transfer of body weight forward to the toes. Proper supination facilitates proper extension of the knee during movement, and is therefore a necessary motion to permit a gait that is both efficient and low in impact shock.
Abnormal supination or pronation typically results in problems within the foot, ankle, knee and even the hip. For instance, hyperpronation, or flatfoot syndrome, has been found in 95% of the patients with total knee replacements. Acquired adult flatfoot arises from numerous causes, including fracture or dislocation, tendon laceration, tarsal coalition, arthritis, neuroarthropathy, neurologic weakness and iatrogenic causes. The most common cause of acquired flatfoot is posterior tibial tendon dysfunction.
Conservative treatment regimes include the use of orthotics to mechanically introduce proper pronation or supination, stretching exercises where the abnormality is due to ligament tension, and medication for pain relief. These conservative approaches may provide enough relief for the patient to assume a near normal gait and level of physical activity, but will not provide any significant correction at the point of contact.
In many cases, surgical correction is necessary to address problems with improper or excessive supination or pronation. For instance, surgical treatments for flatfoot includes tenosynovectomy, osteotomy of the heel bone (calcaneous), tendon transfer, arthrodesis (fusion of adjacent bones), and lateral column lengthening. Of these procedures, the latter is often preferred because it helps realign the bones of the foot and restores a proper arch in the foot.
The Evan anterior calcaneal lengthening osteotomy is one surgical procedure that lengthens the lateral column of the foot by inserting a 10-15 mm bone graft 10-15 mm proximal to the calcaneocuboid joint. This procedure improves forefoot abduction and hind foot valgus, and restores midfoot arch. This procedure is often performed in conjunction with posterior tibial tendon repair or shortening, and deltoid ligament repair or reconstruction as indicated.
In another approach, lateral column lengthening is accomplished through distraction arthrodesis of the calcaneocuboid joint. The procedure is usually accompanied by FDL (flexor digitorum longus) or FHL (flexor hallucis longus) transfer and selective midfoot arthrodesis. In one typical procedure, a 5 cm dorsolateral incision is made over the calcaneocuboid joint and the sural nerve and peroneal tendons are retracted plantarly. The joint is exposed and the articular cartilage removed with osteotomes and curettes. The joint is then distracted using a smooth laminar spreader. Alternatively, a small external fixator is used to distract the lateral column, acting against pins placed in the cuboid and calcaneous bones. Correction of the medial longitudinal arch and the heel valgus to neutral or slight valgus serve as endpoints for the distraction. The forefoot is also rotated into neutral position prior to graft insertion.
The graft material is typically obtained from the iliac crest and then fashioned to fit into the distracted calcaneocuboid joint. In this procedure, the bone graft is typically wider both dorsally and laterally and tapering towards the plantar and medial aspects, respectively. A cervical plate placed laterally with two screws in the calcaneous and two screws in the cuboid complete the fusion. The remainder of the calcaneocuboid joint is then filled with cancellous graft.
One obvious drawback of this known fusion procedure is that it requires an additional surgery to remove the graft material from the iliac crest. Another drawback is that the graft material must be manually shaped to an appropriate shape and dimension during the surgical procedure, which is time-consuming and cumbersome. Finally, these known fusion techniques still require the use of a fixation plate to sufficiently immobilize the joint for arthrodesis to occur.